The present invention relates to the art of image reconstruction. It finds particular application in conjunction with CT scanners, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications.
Conventionally, spiral CT scanners include an x-ray source which projects a thin slice or beam of radiation. The x-ray source is mounted for rotational movement about a subject who is moving along the axis of rotation. An arc or ring of radiation detectors receive radiation which has traversed the subject. Data from the radiation detectors represents a single spiraling slice through the subject. The data from the detectors is reconstructed into a three-dimensional image representation.
For faster data collection, a pair or more of radiation detectors can be disposed next to each other. This enables two or more slices of data to be collected concurrently. However, like the single slice scanner, only intra-slice data is used in the reconstruction process.
One of the difficulties with such prior art scanners is that they place major stress on the x-ray generator. When a solid geometric shape of x-rays, such as a cone, are generated, the x-rays pass through a volumetric region of the subject. In true cone beam reconstruction, truncation of the data is not permitted. These x-rays pass along known rays, both within traditional planes and at acute angles through several planes. The radiation passing along rays at an angle to the central plane were previously lost to collimation. By utilizing the radiation previously lost in collimation to generate useful diagnostic information, the load on the x-ray generator is reduced.
However, images reconstructed from data collected along divergent beams tend to have artifacts. One way of minimizing the divergent ray artifacts is to minimize the number of rings, i.e., limit the width of the cone beam. Of course, limiting the width of the cone beam partially defeats the original intent.
Although the additional radiation supplied by the cone beam is beneficial in imaging, it has the detrimental side effect of increasing the dosage to the subject. On the other hand, the high dosage enables a volume to be reconstructed with fewer rotations of the cone beam.
In U.S. Pat. No. 5,625,660 (hereinafter the '660 patent), commonly assigned and incorporated herein by reference, an image reconstruction technique for helical partial cone-beam data is disclosed. However, that technique divides the data stream into two parts which are processed separately and then recombined. In general, this is less efficient and more complicated than processing a single data stream.
In H. Tuy's U.S. patent application Ser. No. 09/164,013 entitled "3D Image Reconstruction for Helical Partial Cone Beam Data" and filed Sep. 30, 1998 which is commonly assigned and incorporated by reference here, a single data stream image reconstruction technique for helical partial cone-beam data is disclosed. While relatively more efficient and less complicated than the '660 patent, this technique is still somewhat computationally complex and time intensive, leaving room for the development of simpler time-saving techniques.
The present invention contemplates a new and improved image reconstruction technique which overcomes the above-referenced problems and others.